What is an mtDNA transversion? What is the nomenclature for displaying them?

Transversions are types of DNA mutations. They are places in your DNA where nucleotides (Cytosine, Guanine, Adenine, and Thymine) have changed value.

Transversions are where a purine has mutated to a pyrimidine or where a pyrimidine has mutated to a purine (C <-> G, C <-> A, T <-> G, or T<-> A). Transversions are shown by giving the original value capitalized before the location and the mutated value uncapitalized after the location. Thus, a transversion of an A nucleotide at locus 825 to a t is shown as A825t.